Walking through my local grocery store last week, I passed by the aisle with protein bars, granola, and generally healthy-ish snacks, and something caught my attention—a giant "keto-friendly" cookie that proudly proclaimed it had just 3 grams of net carbs on the front of the package. Cool, I thought, I like cookies and I'd rather not jack up my blood sugar.

But flipping over the package revealed that this seemingly innocent cookie had 26 grams of total carbs. What gives?

According to the company, most of those carbs come from allulose—a type of sugar alcohol—which means it basically "doesn't count," as your body can't metabolize it like regular sugar, and some of those carbs come from fiber, which isn't absorbed, so that "doesn't count" either. At least that's what several companies marketing their products to low-carb, keto dieters are claiming. But honestly, it seems too good to be true.

Here, we asked some nutrition experts for their thoughts on net carbs, whether it ever makes sense to count them (as opposed to total carbs), and what might be more important to focus your attention on while sticking to a low-carb diet.

What are net carbs (and how do you calculate them)?

"Net carbs," sometimes referred to as "impact carbs" or "active carbs," isn't a legally defined term. The only type of carb regulated by the Food & Drug Administration is the total carbs you see on the nutrition facts, which is broken down into dietary fibers and sugar.

So, depending on who you ask, you might get a slightly different definition on how net carbs are actually calculated. But here’s the general consensus:

But what's the point of this calculation? The basic concept is that not all carbs are equally absorbed by the body—and thus, they shouldn't be counted. These uncounted carbs are sometimes referred to as "non-impact carbs" or "inactive carbs."

"Net carbs are based on the assumption that fiber in a food is not metabolized or broken down into sugar in the bloodstream," says Ali Miller, R.D., integrative dietitian and ketogenic diet expert. And if it's not broken down into sugar in the bloodstream, that means it won't spike your blood sugar or knock you out of ketosis. Right? While this all sounds great in theory, there are some flaws with the formula, which calls into question how useful this net carb formula actually is.

Article continues below

Are there benefits to focusing on net carbs instead of total carbs?

"One upside to looking at net carbs is that you get an idea of how that particular food might impact your blood sugar, which ties in to how long you feel full and energized," says Jess Cording, R.D., mbg Collective member. For example, a slice of bread and a cup of raspberries have an equal number of total carbs (15 grams), but the raspberries will keep you fuller and happier because they pack significantly more fiber (8 grams vs. 0.8 grams), giving them a lower net carb count (7 grams vs. 14.2 grams).

"That said, that [net carb] number may not be entirely accurate, as the body also absorbs some fiber and sugar alcohols," says Cording. And the whole situation gets very tricky with packaged foods, when companies start adding ingredients, like fiber-rich inulin, for the sole purpose of knocking down that net carb count.

Are there downsides to focusing on net carbs?

The short answer: yes, several. Miller feels quite strongly that focusing on only net carbs isn't an accurate measure of carb intake because the way each individual processes and metabolizes "non-impact" carbs like fiber is different.

"In my 10-plus years of using the ketogenic diet for beneficial metabolic, hormonal, and neurological influences on the body, I have always stuck with total carbs because there are variances in our individual blood sugar responses to fibers, depending on the unique state of our gut bacteria and blood sugar metabolism," she says. "Also, the form of fiber (soluble vs. insoluble) may be metabolized differently, and the source of the fiber in many packaged foods is highly processed and could still yield a blood sugar spike."

And while the net carb formula is likely flawed across the board, it's probably the least useful when it comes to packaged foods. At least with a whole plant food like raspberries, you know that the low net carb number is a result of naturally high fiber content—which is awesome for your health for a number of reasons. But with packaged foods, these added fibers and sugar alcohols are not something your body typically encounters (at least not in such high quantities), which can lead to its own set of issues.

"As soon as the food industry caught on to the value of fiber, they started adding processed industrialized ingredients to packaged foods to increase the total fiber count, but many of these ingredients can be gut irritants," says Miller. "I always say focus on whole food ingredients—the impact of the fiber from leafy greens, avocado, nuts, and seeds is superior to that in a processed product using inulin, corn fiber, or other additives."

Cording agrees, adding that another common issue with tracking net carbs is that it can lead to excessive calorie intake if someone has the idea that they can simply "cancel out" a higher-carb foods with loads of fiber. Plus, on a mental level, tracking net carbs can lend itself to a lot of overthinking and may make it harder for someone to be able to enjoy a balanced meal when they don't know the breakdown of total carbs vs. fiber vs. sugar alcohols.

Bottom line: Net carbs are misleading.

"Net carbs are a misleading and potentially an inaccurate way to monitor carb intake," says Miller, and neither Cording nor Miller recommends that anyone (including low-carb keto dieters) use them to track carb intake.

Instead, both say that keeping a food's total carb count in mind makes a lot more sense if you're watching your carbs. To keep your total carb intake low, your best strategy is to focus on low-carb whole foods such as nonstarchy veggies like leafy greens, high-fiber fruits like berries, healthy fats like olive oil, quality meats and fish, nuts, and seeds.